SIRIUS safety relay input extension Advanced Input extension for an additional 2-channel or two 1-channel sensors Us = 24 V DC Spring-loaded connection (push-in) SIRIUS 3SK1 sensor extension for safety-related extension of the Advanced basic devices.The 3SK1220 sensor extension enables simple and flexible integration of additional sensors into the 3SK system without additional wiring effort between the devices. The device monitors two 1-channel or one 2-channel sensor regardless of the type of output (potential-free or non-floating).The devices are all available with screw or spring-loaded connection (push-in).The 3SK safety relays replace the proven 3TK28 series.Safety is a SIRIUS business.